Power Capacitors are first class, got all me invertors and motors through them. Used to be agents for Eurotherm drives. They are now made by Parker SSD. Me oldest Eurotherm 650 drive is 15 / 16 years old now and never one single issue in that time. WEG are also first class VFD's .

cheers.

Try

Gavin Oseman
Malvern
WR14
UK
01684 574966
hpdrifter@outlook.com

Transwave part of Power Capacitors. Top notch. Robert, the Eurotherm 650 series of the correct rating will suit your motor. I can't praise these drives high enough Eurotherm, WEG, Siemens. Never a glitch in all the years. i've used them. I have no experience of any other makes.

Just a suggestion but why not ebay?

I have 3 inverter drives , all new boxed ,fitted to 2 lathes and most recently a mill. Previous to that i had no experience of inverter drives.

All three motors were off ebay as well and were brand new .

My smallest lathe a pultra ,cost me £70 for the Brookes motor and Mitsubishi inverter.

The Southbend ,cost £130 for a Brookes 3/4 HP and a Siemens 440 inverter.

My latest purchase a mill ,i fitted with a 2 HP GE Electric washdown motor and Toshiba inverter cost £280

No complaints how any of the motors or drives are working and for 3 machines £480 is hard to beat.

Edited By mark smith 20 on 20/10/2016 19:24:14

I'll add to your comments if I may Roderick.

​Newton Tesla told me some while ago that inverters require a small but measurable leakage to earth (approximately 10 mA ) to function correctly; without it the motors sound metallic.

​At the time of asking, we were still operating with tower block computer systems that had no possibility of saving work in the event of a power shutdown from the earth leakage trip. The house also supplied power to pond pumps in the garden that are notoriously 'lossy' things. Any further sources of leakage were quite likely to trip out the house supply and I carried on without making the change.

​Since that time, the workshop supply has been changed to one through a new dedicated earth leakage trip with it's own reference earth rod, completely isolated to the one that the house trip is referenced back to and the problem no longer exists. Lack of funds is the reason now for not taking advantage of that change!

​Brian

"I have a consumer unit in the workshop fed from the house via armoured cable. The consumer unit in the workshop came with a on /off power mcb? type switch which i changed to a 30ma RCD switch years ago."

That part in the above post i think should read changed to a ELCB,this is what i fitted in the consumer unit.

Edited By mark smith 20 on 21/10/2016 19:23:12

Inverter drives are certainly not easy to understand once you get past the basic stuff.

My manual says you can reduce the PWM carrier frequency down to a minimum of 2KHZ which can stop ELCB `s from misbehaving . But also says you can get more motor noise. I`ll have to figure out how to reduce that and see if anything happens???

The manual also says you can use interference proof ELCB`s ,and then you can increase the PWM carrier frequency?

What i dont understand is why its tripping when i turn the isolator to the off position.

Thanks

Edited By mark smith 20 on 21/10/2016 19:43:26

A couple of points regarding problems that some invertor users have highlighted in this thread:

1. All invertors will produce an amount of earth leakage when used.

2. Earth Leakage is "cumulative" , your household electricity system may already be producing some leakage but below the 30ma trip level, adding an invertor may push it "over the edge" and trip your supply .

3. The most common items in your house that can be producing earth leakage are cookers, kettles and water heaters, devices with older brush equipped motors (washing machines) that have gone through a couple of sets of brushes also tend to have a bit of leakage – if you are having problems with your inverter tripping the supply try switching off these devices – a bit of detective work can sometimes reveal a "leaky" device .

4.When fitting an invertor drive the cable between the invertor and the motor should be a screened type. The screen is there to prevent interference and should be earthed at one point only.

5. A 110 volt transformer is unlikely to produce earth leakage but it can suffer from saturation, depending on a few different factors, when it is switched on it can trip the circuit breaker, this is based on a current overload and not earth leakage.

Hope this helps with a few peoples experiences

Martin

Martin's advice that earth leakage is cumulative just woke me up.

These days the average house is likely to have a lot of devices fitted with EMI filters plugged into the mains more or less permanently. TV sets, computers, radios, routers, white goods, heaters, air-con, telephone answering machines, video recorders, hifi systems, lighting etc etc. Together that little lot could be leaking enough to put an RCD close to the edge.

It would be useful to know. Can anyone suggest a safe way of measuring earth current leakage at the consumer unit? (I think simply cutting the earth cable to insert an AC ammeter would be unwise!)

Dave

This all seems a little murky!

I'm pretty sure that you can't buy an ELCB any more. Someone is bound to prove me wrong, but broadly I would declare the ELCB technology obsolete. They work differently from RCDs although they do a similar job. An ELCB actually measures earth current. In situations like "TT" supplies where an actual ground spike is the only method of grounding, the ground impedance can vary wildly. If the ground potential does vary, it can render the ELCB useless, and no one will know.

RCD technology compares supply and return current. It calculates the difference and infers the earth current, even if that current is not passing through the earth conductor. It requires no earth connection and helps to make "TT" supplies much safer.

All modern switch mode supplies (of which inverters are a kind) usually require some kind of EMC filter to allow then to pass conducted emissions tests and gain CE and other approvals.

EMC filters work by providing a high frequency path from the live and neutral conductor down to ground. Generally the impedance of an EMC filter from LN to E is fairly high. Indeed there is normally some leakage even in a simple electrical appliance with a line transformer. Typically the coupling is capacitive from the primary into the frame of the of the transformer.

It from the perspective of the RCD these leakages can accrue. If you have a single RCD on a whole premises, then it is possible that all of the leakages can accrue to the point where nuisance tripping occurs.

In general, nuisance tripping of RCD's is much less pronounced than it is for the old, less safe, ELCB technology.

Most appliances leak much less than their allowable class limit, but it is a particular problem with motor inverters, because we all want nice (sonically) quiet motor drives. In order that the switching noise cannot be heard in the windings of the motors we all wind up the switching frequency so that it is outside of the audible range.

The downside to this is that it pushes electrical energy out into the network at frequencies which are quite tightly controlled. The regulatory authorities consequently demand EMC filters to prevent this from happening.

The EMC filters for motor inverters are usually quite big, because AC induction motors are a heavy load. The electrical noise is powerful and at high frequency. These signals can interfere more easily with radio systems. Appropriate EMC filters can leak quite a lot.

Most loads are not big motors.

In your workshop, you probably only need one inverter running at a time. If they have a proper isolator, then they probably don't all need to be connected at the same time. If they are not all connected at the same time, then their EMC filters cannot accrue leakage.

Decent inverters usually have selectable EMC filters. I bought a Schneider, and it says that if you disable the EMC filter then you should run it at a low switching frequency, to remain compliant. Sure you can hear the motor hum but so what. Mine actually has a dynamic mode. If the load increases, the switching frequency reduces. This maintains compliance, and is quiet most of the time. I actually quite like it. I get feedback about how I am loading the motor, by the sound it makes.

I commissioned a medical robot a while back which had several powerful (>1HP) axes, all of which had their own inverter. Obviously the axes all had to be on at the same time to achieve co-ordinated motion. Being a medical robot it had to be compliant. The answer was to provide external EMC filters. A single combined filter does not have to have the same leakage as the sum of each filter together.

Conducted emissions are only high when the motor is loaded. It is not likely that all axes will be maximally loaded at the same time. Even if they are, it is only a temporary situation.

Increasingly electrical switchgear manufacturers are promoting RCBO's. These provide discrete RCDs combined with traditional thermal-magnetic breakers. Instead of having a single RCD each "fuse" has its own. By using these RCBO devices, accrual of leakage can be managed, and nuisance tripping reduced.

In high load situations perhaps greater than 50A it might be the case that it is hard to find an RCD capable of the job. It should always be remembered that inverter systems can often be isolating.

The isolating nature prevents the controlled AC voltage generated from being directly hazardous. Clearly, if a circuit with no RCD protection is used and used in a fixed wiring scenario (supply side trunking/conduit) then safety hazards are inherently constrained.

Obviously no RCD with a non-armoured trailing cable has its hazards.

Andy.

Edited By Andy Ash on 21/10/2016 23:09:31

Well done, Andy Ash, some sensible rmarks at last! Many of the comments regarding RCD's show a complete misunderstanding of their function and, indeed, where they are required under the current wiring regs.

If you are running a sub-main to a garage / workshop via, for example, a SWA cable then there is no requirement to RCD-protect that cable. Modern consumer units allow for unprotected ways and the submain should be taken from this section, the regs require that the cable is suitably protected and the armouring, earthed at the source, provides this protection. The RCD should be at the next port of call i.e. the garage / workshop consumer unit.

30mA RCD protection is for "person protection", in other words to try to save your life if you receive an electric shock. They compare the current flowing in the line and the neutral conductors which should be perfectly in balance. If there is less current returning in the neutral than went out in the line (or live, as we used to call it) then it is going somewhere else – probably through you to earth. This imbalance trips the RCD before your heart goes into fibrillation.

Another thing to note is that RCD's do not discriminate. If there are two 30mA RCD's in series and a >30mA leakage occur, then both RCD's will trip. Electricity moves, to all intents and purposes, at the speed of light and the mechanics of an RCD cannot act quickly enough to ensure that the unit closest to the fault switches off before the other(s) follow suit. Another reason to ensure that the supply cable to your workshop is NOT protected at the house end.

Caveats: if the workshop supply cable is just some T&E then extra protection, such as conduit may be advisable. If the supply is TT (you have one or more earth rods) then there may be a front-end 100mA RCD. This is not the same as a 30mA RCD and has a different function, it is there for fire protection. The advice is that the heart goes into fibrillation at about 40mA and a 100mA RCd is, obviously, not going to be much protection to you if you are unfortunate enough to receive an electic shock. A 30mA RCD and a 100mA RCD WILL discriminate if the fault current is less than 100mA but, otherwise, both will trip as will two or more of the same rating.

If contemplating setting up a new workshop, it is well worth talking to your local spark. It could actually save you money, and it may save your life if things go pear-shaped. But, hey-ho, we're engineers and know it all, dont we?

Steve